Fix a number of push notification issues

[astralbodies]

Fixes #961

Still can't reproduce the problem with credentials being lost on the device after a background push was received. Discovered a number of problems with push, however, and have resolved them in this PR.

1. Background pushes should not be updating the UI (if possible) since we also refresh data when the UI is presented for notifications.
2. Background pushes have the ability to launch the app in iOS 7 - with the side effect of that push being sent through the options dictionary. The UI is now not updated in that case.
3. When we unregister a device with our backend push server we should really also be unregistering with Apple's push network.
4. All of our launch work was being done in willFinishLaunchingWithOptions - UI work should really be done in didFinishLaunchingWithOptions. Moved the key window call and notification handling to the delegate method called after the app is running.
5. WordPress.com API was not calling unregister for push when logging out the main WP.com account. Probably shouldn't be handled in the API since we're going to make it a Pod but it can't be eliminated from this release. Marked as a FIXME.

[pivotal-rebecca]

4 - it's being called on logout in 22-accounts I believe.

1 - the background pushes were updating the UI to use iOS7's multitasking features. When the completion handler is called, a screenshot is taken of the current state. Granted, you may not be on the notifications screen :) Perhaps if you are, we should update the UI?

[astralbodies]

@xtreme-rebecca-putinski I reversed the change made to the WordPress.com API for unregistering notifications.

Yeah I think I'm going to put the Notifications screen UI changes into another ticket, because some cleanup is going to be needed. Hooking into the will/did/Appear/Disappear is hokey especially with the background updates.

[sendhil]

@astralbodies - Did you mean to get rid of the mixpanel call as well?

[astralbodies]

I removed it since this is fired off and has no user interaction (app didn't actually open)

[sendhil]

Ahhh - can we move it to someplace where the user does have interaction - i.e. https://github.com/wordpress-mobile/WordPress-iOS/pull/1000/files#diff-12c33a973ac67adb445a57af0d26b92cR128?

[astralbodies]

@sendhil It is being handled in this method - sorry it took me forever to verify 😄

WordPress-iOS/WordPress/Classes/NotificationsManager.m

Line 132 in 67864b1

+ (void)handleNotificationForApplicationLaunch:(NSDictionary *)launchOptions {

[sendhil]

@astralbodies - awesome, thanks for that.